@Jurek&: great idea for a thread! I started a "Polar Bear Exhibits" thread a while ago and there were a load of responses, and so an "underwater views" thread is bound to get some interest.
@jwer:there has also been a huge investment in elephant exhibits in North America, as more than 40 zoos out of the approximately 80 that have elephants have recently updated their enclosures. I really don't know why European zoos don't have an emphasis on polar bears...
After a brief search I found 12 North American zoos with underwater viewing of polar bears. Maryland, Detroit, Pittsburgh, Central Park, Memphis, Cincinnati, Toledo, Denver, San Diego, Point Defiance, Oregon, and Rio Grande. Plus the Seaworlds and so there must be at least 15 establishments with underwater viewing.
On top of that, there are at least another 9 zoos that have either already started building or are awaiting funding for polar bear exhibits with underwater viewing. Toronto, Calgary, Roger Williams Park, Kansas City, Henry Vilas, Buffalo, Columbus, Louisville and North Carolina.